JP2005252106A - Semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device including a red semiconductor light emitting element capable of solving problems of an operating current and a kink level. <P>SOLUTION: Projections 16, 17 opposing to both side faces of a ridge 14 acting like a principal current path and each including an intermediate layer 9 and a current blocking layer 11 are formed to a laminated semiconductor layer 20 in a direction orthogonal to the laminated direction of the layer 20. The symmetry of light can be enhanced even in the case of employing an off-substrate by adjusting the width of ridge groove 12 (13) reaching the projection 16 (17) from one of both the side faces of the ridge 14. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is applied to a semiconductor light emitting device, in particular, a semiconductor device having a red light emitting pulsation laser, for example, a red light emitting pulsation laser alone or a semiconductor light emitting device having a semiconductor light emitting element of this red light emitting pulsation laser and other wavelengths. The present invention relates to a suitable semiconductor light emitting device.

  As the recording / reproducing laser light for the optical information recording medium, it is desirable to use a pulsed laser light source in order to improve noise caused by the return light. Furthermore, it is desirable to use a pulsation laser by self-excited oscillation that does not perform this pulse oscillation by an external circuit.

A laser light source having a wavelength of 780 nm is generally used for an optical information recording medium such as a CD (Compact Disc), and a laser light source having a wavelength of 650 nm is generally used for a DVD (Digital Versatile Disc). .
As a red pulsation semiconductor laser having a wavelength of 650 nm, for example, an AlGaInP semiconductor laser has been proposed (see, for example, Patent Document 1).

For example, FIG. 4 shows a schematic perspective view of this AlGaInP-based semiconductor laser, and FIG. 5 shows a schematic cross-sectional view of the main part thereof. As shown in FIG. A first conductivity type clad layer 104 made of AlGaInP of the first conductivity type, for example, n-type, an active layer 105 having a multi quantum well (MQW) structure of, for example, GaInP and AlGaInP, A clad layer 106 made of a conductive type, for example, p-type AlGaInP, and a contact layer 110 made of a second conductive type, for example, p-type GaAs, are epitaxially grown sequentially.
Then, ridge grooves that cross the contact layer 110 and reach the second conductivity type cladding layer 106 are formed on both sides, thereby forming a stripe-shaped ridge 114.
A first electrode 118 is ohmic deposited across the ridge from the ridge groove, while a second electrode 119 is deposited on the back surface of the substrate.

In the semiconductor laser having this configuration, pulsation laser oscillation is performed by applying a forward voltage between both electrodes.
That is, in this case, since the contact resistance is smaller in the portion where the second electrode is in contact with the contact layer than in the portion directly deposited on the cladding layer, a main current path is formed in the stripe portion formed by the ridge. Is done. In this case, as schematically shown by the broken line a in FIG. 5, the thickness of the second conductivity type cladding layer is different between the ridge groove forming portion and the ridge, and the current injection is mainly performed in the ridge. Therefore, an effective refractive index difference is generated between the central portion below the ridge and the outside thereof, and a main light emission distribution due to gentle light confinement is formed in the central portion, and a saturable absorption region is formed outside thereof. As a result, self-excited oscillation is generated.
JP 2002-76505 A

  However, in general self-excited oscillation type lasers including those having the above-described air ridge pulsation laser structure, current is diffused in addition to the main current path forming portion as schematically shown by arrows in FIG. Therefore, this current becomes a reactive current that does not contribute to oscillation, and the operating current increases. In addition, there is a problem that the long-term reliability and the lifetime are lowered.

  In addition, in an AlGaInP semiconductor laser as a semiconductor laser having an oscillation wavelength band of 650 to 660 nm used for a DVD, the MQW constituting the active layer is a natural superlattice when the AlGaInP / GaInP structure is used as described above. As a result, the band gap is reduced and the oscillation wavelength is increased. In order to avoid such an inconvenience, in this type of AlGaInP semiconductor laser, the main surface of the GaAs substrate as a base is usually cut out with an inclination of 2 ° to 10 ° from the (001) crystal plane. By using an off-substrate, the generation of a natural superlattice structure is avoided and a longer wavelength is avoided.

  However, when such an off-substrate is used, both ends in the stripe direction, that is, both ends in the optical resonator length direction are formed by the cleavage planes of the crystal, so that an excellent mirror surface can be formed. When the direction is selected and the ridge groove is formed by wet etching, as shown in FIG. 5, the slopes on both side surfaces of the ridge are different and asymmetric.

  For this reason, the refractive index difference of the waveguide portion is different on both sides of the light emitting portion, the light confinement becomes asymmetric, the light emission distribution becomes asymmetrical, as shown by the broken line b in FIG. Low level kinks occur.

  The present invention provides a semiconductor light emitting device capable of solving the above-described problems, that is, the problem of operating current and the kink level in a semiconductor light emitting device having a red semiconductor light emitting element.

  A semiconductor light emitting device according to the present invention is a semiconductor light emitting device having a red light emitting pulsation laser, and comprises at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer on a substrate. A stripe portion formed by a ridge formed between the ridge grooves via a ridge groove having a depth that does not reach the active layer from the side opposite to the active layer of the stacked semiconductor layer. A protrusion that extends from the ridge groove and extends along the stripe portion so as to face both side surfaces of the substrate, and a main current path to the active layer is formed in the stripe portion to form a main light emitting portion. A saturable absorption region is formed on both side edges of the light emitting portion, and a current blocking pn junction is formed on the protrusion.

  The semiconductor light emitting device according to the present invention is characterized in that the distance between the stripe portion and the protrusions facing both side surfaces of the stripe portion is selected to be different from each other.

  The semiconductor light-emitting device according to the present invention is characterized in that the substrate is made of a semiconductor off-substrate whose plate surface has a required inclination from the {100} crystal plane.

  According to the semiconductor light emitting device of the present invention, the protrusions are provided facing both side surfaces of the stripe portion by the ridge forming the main current path, and the current blocking pn junction is provided on this, so that the region other than the laser oscillation region is provided. Therefore, the generation of reactive current is reduced or avoided, which leads to a reduction in operating current. The current blocking at the protrusion is performed by the presence of a pn junction, specifically, a pn junction that is reversely connected during operation. The pn junction is formed in a series of manufacturing processes of the semiconductor layer. Therefore, the complexity of the manufacturing process when the current blocking layer is formed of an insulating layer can be avoided, and the heat conduction is generally better than that of the insulating layer, so that the laser can be operated. Can be effectively dissipated.

  Further, according to the semiconductor light emitting device of the present invention, the widths of the ridge grooves on both sides of the ridge are mutually changed, so that the effective refractive index difference between the main light emitting part formed by the main current path and the both sides is equalized. As a result, the asymmetry of the shape of the laser beam and the laser oscillation region that occurs when the semiconductor light-emitting device is configured using the above-described off-substrate as the substrate can be reduced or avoided.

Further, by reducing or avoiding the asymmetry of the laser beam, the kink level is improved by selecting the distance from the stripe to each protrusion, and therefore the long-term reliability and the reduction of the lifetime are reduced or avoided. .
As described above, according to the configuration of the present invention, important and many effects can be brought about.

  Hereinafter, embodiments of a semiconductor light emitting device having a semiconductor laser according to the present invention will be described with reference to the drawings. However, it goes without saying that the semiconductor light emitting device according to the present invention is not limited to this embodiment. .

  First, the structure of an example of a semiconductor light emitting device having a semiconductor laser according to the present invention will be described with reference to FIG. 1 illustrating the red semiconductor laser portion.

In this semiconductor light emitting device 1, a buffer layer 3 of a first conductivity type, for example, n-type GaInP, and a first conductivity type, for example, n-type, are formed on one main surface of a substrate, for example, a first conductivity type, for example, n-type GaAs substrate 2. A clad layer 4 made of AlGaInP, an active layer 5 made of, for example, a multiple quantum well (MQW) structure of GaInP and AlGaInP, and a lower clad layer 6 constituting a lower layer portion of a clad layer made of a second conductivity type, eg, p-type AlGaAs, Etching stop layer 7 of the second conductivity type, for example, p-type GaInP, upper clad layer 8 constituting the upper layer portion of the second conductivity type, for example, p-type AlGaInP, and second conductivity type, for example, p-type GaInP An intermediate layer 9 formed of the second conductive type, for example, a p-type contact layer 10, and a first conductive type, for example, an n-type AlGaInP. A layer 11 is formed by sequentially epitaxially grown stacked semiconductor layer 20 is formed. Then, ridge grooves 12 and 13 whose depths are regulated by an etching stop layer are formed from the contact layer side of the laminated semiconductor layer 20 as will be described later.
The ridges 14 formed between the ridge grooves 12 and 13 are opposed to both side surfaces of the stripe portion constituting the main current path, and are respectively maintained at predetermined intervals L ₁ and L ₂ from the grooves. As a result, protrusions 16 and 17 extending along the stripe 15 or ridge are formed.
The ridge constituting the main current path has a configuration in which the current blocking layer of the stacked semiconductor layer 20 described above is removed.

  Then, on the laminated semiconductor layer 20, the first electrode 18 is ohmicly deposited on the entire surface including the ridge grooves and protrusions on both sides of the ridge, and the second electrode 19 is ohmicly deposited on the back surface of the substrate. It consists of

As a manufacturing method of the apparatus of the present invention described above, for example, a process shown in FIGS. 2A and 2B can be used.
First, as shown in FIG. 2A, a GaAs substrate 2 having, for example, an inclination of 2 ° to 10 ° from an n-type {100} plane is prepared as a substrate, and a buffer layer made of, for example, GaAs is formed on one main surface as necessary. 3 through the first conductivity type, for example, the n-type clad layer 4, the active layer 5 made of, for example, MQW, the lower clad layer 6 of the second conductivity type clad layer, the etching stop layer 7, and the second conductivity type. A laminated semiconductor layer 20 is formed by sequentially epitaxially growing an upper clad layer 8, a second conductivity type intermediate layer 9, and a second conductivity type contact layer 10 of the second clad layer.
Next, as shown in FIG. 2B, the current blocking layer immediately above the region where the ridge and the ridge groove are formed with an acetic acid-based etching solution so as to leave at least the formation portions of the protrusions 16 and 17 described in FIG. 11 is selectively removed by etching.
After that, as shown in FIG. 3, the contact layer 10 is made of a phosphoric acid etching solution, the intermediate layer 9 is made of an acetic acid etching solution, the second conductivity type cladding layer 8 is made of sulfuric acid, and the etching stop layer 7 is etched by, for example, photolithography. Are etched with an acetic acid-based etchant to form ridge grooves 12 and 13, together with which ridges 14 and protrusions 16 and 17 are formed. At this time, the etching stop layer 7 made of GaInP has a much slower etching rate than the second conductivity type cladding layer 8 made of AlGaInP. Control to stop at the position where 6 is exposed can be easily performed.

Thereafter, the first electrode is brought into full contact with the ridge 14 and the ridge grooves 12 and 13. The second electrode 19 is in ohmic contact with the back surface of the substrate 2.
The first electrode 18 can be configured using a multilayer metal layer of Ti / Pt / Au.
The second electrode 19 can be configured using a multilayer metal layer of AuGe / Ni / Au.

  Thus, the semiconductor light emitting device 1 using the red semiconductor laser according to the present invention shown in FIG. 1 is constructed.

As this base body or substrate 2, for example, a so-called semiconductor off-base body or substrate having a required inclination of 2 ° to 10 ° as described above from the {100} crystal plane can be used.
Since the base | substrate 2 is an off board | substrate at this time, the inclination of the both sides | surfaces of a ridge is asymmetrical. In the present invention, for example, the inclination of the left side surface in FIG. 3 is gentler than the inclination of the right side surface. In this case, the left interval L ₁ is larger than the right interval L _{2 in} FIG. For example, by selecting L ₁ = 40 μm and L ₂ = 15 μm, respectively, the asymmetry of the light distribution due to these inclinations can be compensated. That is, by selecting the distance from the stripe portion 15 to each protrusion, the effective refractive index difference between the central portion below the ridge and the outside thereof is compensated, and the kink level is improved.

In the semiconductor light emitting device 1 according to this embodiment, the current supplied between the first electrode 18 and the second electrode 19 is limited to the ridge 14 and the ridge grooves 12 and 13 by the protrusion and the current blocking layer. The reactive current is blocked. Therefore, the operating current can be reduced.
Then, the protrusions 16 and 17 are constituted by the second conductivity type of the intermediate layer 9 and the current blocking layer 11 such as p-type GaAs and the first conductivity type such as n-type AlGaInP, so that the first electrode 18 is formed. In addition, a current blocking pn junction (reverse junction) is formed with respect to the second electrode 19, and a sufficient current blocking action, that is, a current limiting action on the ridge grooves 12 and 13 and the ridge 14 is obtained. In this case, a special process is not used as in the case where the current blocking layer 11 is made of an insulating material because of a semiconductor manufacturing technique using a pn junction.
In this configuration, the ridge 14 in which the first electrode 18 is in direct contact with the contact layer 10 is more energized than the portion where the contact layer in the ridge grooves 12 and 13 does not exist, and the ridge 14 The main current path to the active layer 5 is formed, and the main light emitting part as shown by the broken line a is formed. Saturable absorption regions are formed at both side edges, and pulsation laser operation occurs.

  The above-described embodiment of the semiconductor light emitting device according to the present invention has been described by exemplifying a red light emitting pulsation laser. However, the semiconductor light emitting device according to the present invention includes, for example, a red light emitting pulsation laser and semiconductor light emission of other wavelengths. The present invention can also be applied to a two-wavelength type or multiple-wavelength type semiconductor light emitting device having an element such as a pulsation laser. The semiconductor light emitting device according to the present invention can also be applied to the red portion of a two-wavelength monolithic laser.

  The present invention is not limited to this embodiment, and it goes without saying that various modifications and changes can be made.

For example, in this embodiment, the saturable absorption region (SAR) is provided in the active layer (so-called weakly index guide type; WI type). However, in the semiconductor light emitting device 1 according to the present invention, A so-called SAL (Saturable Absorbing Layer) type pulsation laser in which a separate SAR is provided in the vicinity of the active layer can also be used.
Further, the current blocking layer can also exhibit a current blocking action by forming it with an insulator.

  In this embodiment, the first conductivity type is mainly n-type and the second conductivity type is p-type. However, it is within the scope of the present invention that both are reversed. It will be appreciated by those skilled in the art that the device can be variously modified and modified.

1 is a schematic perspective view of an air ridge pulsation laser as an example of a semiconductor light emitting device according to the present invention. A and B are schematic cross-sectional views in the manufacturing process of an air ridge pulsation laser as an example of a semiconductor light emitting device according to the present invention. It is a schematic sectional drawing which shows the structure of the principal part of an air ridge pulsation laser as an example of the semiconductor light-emitting device by this invention, and the state of the light distribution in the inside. It is a schematic perspective view which shows the structure of the conventional semiconductor laser which is 1 type of a common semiconductor light-emitting device. It is a schematic sectional drawing which shows the structure of the principal part of the conventional air ridge pulsation laser, and the state of the light distribution in the inside.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor light-emitting device, 2 ... Base | substrate (substrate), 3 ... Buffer layer, 4 ... 1st conductivity type clad layer, 5 ... Active layer, 6 ... 2nd conductivity type Cladding layer (lower layer), 7 ... Etching stop layer, 8 ... Second conductivity type cladding layer (upper layer), 9 ... Intermediate layer, 10 ... Contact layer, 11 ... Current blocking layer, 12 ... Ridge groove, 13 ... Ridge groove, 14 ... Ridge, 15 ... Stripe part, 16 ... Projection part, 17 ... Projection part, 18 ... First electrode, 19 ... Second electrode, 20 ... Laminated semiconductor layer, 101 ... Conventional semiconductor light emitting device, 102 ... Substrate (substrate), 104 ... First conductivity type cladding layer, 105 ... Activity Layer, 106... Second conductivity type cladding layer, 110 contact layer, 114... Ridge, 115. Type unit, 118 ... first electrode, 119 ... second electrode

Claims (3)

A semiconductor light emitting device having a red light emitting pulsation laser,
A laminated semiconductor layer comprising at least a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer on a substrate;
Opposite the opposite side surfaces of the stripe portion by the ridge formed between the ridge grooves through the opposing ridge grooves that do not reach the active layer from the side opposite to the active layer of the laminated semiconductor layer And having a protrusion rising from the ridge groove and extending along the stripe portion,
In the stripe portion, a main current path to the active layer is formed to form a main light emitting portion, and a saturable absorption region is formed on both side edges of the main light emitting portion,
A semiconductor light-emitting device, wherein a current blocking pn junction is formed on the protrusion.   2. The semiconductor light emitting device according to claim 1, wherein an interval between the stripe portion and the protrusion facing the both side surfaces of the stripe portion is selected to be different from each other. 3. The semiconductor light emitting device according to claim 1, wherein the substrate is made of a semiconductor off-substrate whose plate surface has a required inclination from the {100} crystal plane.

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